When uranium is leached from ores during solution mining the hexavalent uranium dissolves into the solution as the stable uranyltricarbonate complex anion, UO.sub.2 (CO.sub.3).sub.3.sup.4-. The tetravalent uranium found in ores such as coffinite, pitchblende, and uraninite does not dissolve in the leaching solution and must be oxidized to the soluble hexavalent state. Chemical oxidants such as hydrogen peroxide, sodium hypochlorite, and potassium permanganate can be used for this purpose but they are expensive and difficult to regenerate.